Membranes have been widely used in chemical analysis. Cortes and Davis, U.S. Pat. No. 4,529,521, used membranes to determine components of interest in latex serum. Stevens, Jewett and Bredeweg, U.S. Pat. No. 4,751,004 used membranes to suppress an Ion Chromatography eluent. Morabito, Melcher, Hiller and McCabe, U.S. Pat. No. 4,962,042 used membranes in a Gas Chromatography system. Stevens, Frawley, Swart, Harris, Diedering, Nicholson and Rothman, U.S. Pat. No. 4,837,161, used membranes to add reagent to a Flow Injection Analysis carrier stream. Melcher and Burr, U.S. Pat. No. 4,913,821, used membranes in a phenol analyzer. Melcher and Cortes, U.S. Pat. No. 4,775,476 described a Liquid Chromatography system employing a membrane, the membrane partitioning a sample from a flowing stream of an extractant, a component of interest permeating across the membrane from the sample into the extractant. Melcher and Cortes also described that the flow of the extractant could be stopped to increase the concentration of the component of interest in the extractant. Yalvac, Melcher and Bredeweg, PCT International Publication Number WO 92/15012, used membranes to determine organic acids. Flow through membrane probes are known in the art of membrane chemical analysis.
The apparatus used in membrane chemical analysis systems typically includes a number of valves. However, when a membrane chemical analysis system is used to analyze a chemical process stream and is installed in the process area, i.e., on-line analysis, then the valves can require more maintenance than is desired especially if the valves are multiport valves. It would be an advance in the art of membrane chemical analyzers if the number and complexity of the valves used could be reduced.